PIIENYLPROPENE DERIVATIVES WITH NITROUSACID
Nov. 20, 1957
[CONTRIBUTION FROM THE
DEPARTMENT OF BIOCHEMISTRY, YALE
595 1
UNIVERSITY]
Reactions of Phenylpropene Derivatives with Nitrous Acid1 BY CHRISTINEZIOUDROU~ AND JOSEPH S. FRUTON RECEIVED JUNE 26, 1957 Several reactions of p-hydroxyphenylpropene derivatives with nitrous acid have been studied. Dehydrodiisoeugenol and a polymeric compound were obtained from isoeugenol, and a dehydropolymer was obtained from p-coumaryl alcohol. X h e n treated with nitrous acid, p-hydroxychalcones yield nitro derivatives. T h e possible relation of the oxidative action of nitrous acid on p-hydroxyphenylpropenes t o the formation of lignin precursors is discussed.
The finding that p-hydroxycinnamic acid (pcoumaric acid) is oxidized readily by nitrous acid a t acid pHvaluesI3andthe widespread occurrence, in plant tissues, of nitrate reductase, led to the suggestion3 t h a t the nitrite generated by the enzymic reduction of nitrate may participate in the oxidation of phenylpropene derivatives currently believed to be precursors of the natural lignin^.^^^ I n attempts to approach the problem of lignin biosynthesis, previous investigators have examined the action of mild oxidants (FeC13, 0 2 , Hz02)on selected phenylpropene derivatives (isoeugenol, coniferyl alcohol, ferulic acid, eugenol, etc.). Of special interest are the studies of Erdtman6 and of Freudenberg7 who showed t h a t the oxidation of isoeugenol by FeC13 leads to the formation of the dimeric compound dehydrodiisoeugenol (I), whose structure 2-(4'-hydroxy-3 - methoxyphenyl) - 3 -methyl- 5 - propenyl- Tmethoxycoumaran was established by degradation studies. OCH3
&')-=-OH
/
monomethyl ether. I n addition, a less well-defined product (softens a t 90-110°) was obtained from the reaction mixture; a molecular weight determination of this material suggested that it may be composed, on the average, of six Cg-units joined together. Like soluble lignins, the polymer gave a dark red color with the phloroglucinol-HC1 reagent. The possibility exists, therefore, that the material contains lignin-like substances formed by the polymerization of oxidized Cg-units. I t will be noted from Fig. 1 t h a t the shift in the absorption maxima for isoeugenol (25s mp, molar absorbance 14,800), dehydrodiisoeugenol (273 mp, molar absorbance 18,200) and the 90-110' product (282 mp), also is in accord with the view that the two latter compounds represent different stages in the polymerization of oxidized isoeugenol. Calculation of the molar absorbance per Cg-unit (assumed molecular weight 108) a t their respective maxima gives the following values : isoeugenol, 9,500; dehydrodiisoeugenol, 6,100; the 90-1 10' product, 2,380. I
An analogous dimeric coumaran derivative was isolateds after the action of 0 2 on coniferyl alcohol a t pH values near 6, in the presence of an enzyme preparation from mushrooms. Such dimeric compounds have therefore been considered to represent intermediates in the polymerization of oxidized phenylpropene derivatives to the polymeric lignin^.^ I n view of these results, and their possible importance for the problem of lignin biosynthesis, i t seemed of interest to examine the action of nitrite on isoeugenol and related phenylpropene derivatives. It was found that, a t p H 6, nitrite readily effects the conversion of isoeugenol to dehydrodiisoeugenol; a yield of 35-40y0 of the theory was obtained under the conditions described in the Experimental section. The identity of this product with t h a t described by Erdtman6 was established by the analytical data, and by the melting points of the product, of the p-nitrobenzoyl ester, and of the (1) T h i s work was supported b y grants from t h e Rockefeller Foundation a n d f r o m t h e National Science Foundation. (2) Postdoctoral Fellow of t h e Greek Fellowship Foundation. (3) C. Zioudrou, W. L. Meyer a n d J. S. F r u t o n , THISJOURNAL, 79, 4114 (1957). (4) K. Freudenberg, Angew. Chern., 68, 84, 508 (1956). ( 5 ) S. M. Siegel, Quant. Rev. B i d . , 31, 1 (1956). (6) H. E r d t m a n , Biochem. Z . , 268, 172 (1933); A n n . Chcm., 503, 283 (1933). (7) K. Freudenberg a n d H. Richtzenhain, ibid., 562, 126 (1942). (8) K. Freudenberg a n d H. H. Hiibner. Ber., 86, 1181 (1952). (9) K . Freudenberg, Forlsch. Chem. oug. N a h r s t o f l e , 11, 43 (1954).
I
I
LLi 0.8 0
z
a m
0.6
[r
0 c/)
m 0.4
a
0.2 240 260 280 300 WAVELENGTH, mp. Fig. 1.-Absorption spectra of isoeugenol, 5 X 10-5 r l l (curve A ) ; of dehydrodiisoeugenol, 5 X lob5 ;\I (curve B ) ; and of polymer (15.1 mg. per liter) formed by the action of nitrite 011 isoeugeiiol (curve C ) ; solvent, 95% ethanol, 1-cm. cells.
Treatment of p-coumaryl alcohol with nitrite (2 moles of nitrite per mole of alcohol) a t p H 6 gave a water-insoluble product whose absorption spec-
CIIKISTINEZIOEDKOUA N D
3932
trum resembled that reportedsofor the polymer obtained by treatment of p-coumaryl alcohol with a mushroom extract a t pH 7. The molar absorbance of p-coumaryl alcohol a t 260 mH is 20,000 (Fig. 2) ; when calculated per Cg-unit, its molar absorbance is 14,000, and t h a t of the polymer formed in the presence of nitrite is 5,100 a t 265 m,u (Fig. 2). I n addition to the decrease in absorbance per Cg-unit, comparison of two spectra shows an almost complete disappearance, in t h a t of the polymer, of the characteristic absorption band a t 293 mp of the ethylenic double bond. -4 control experiment a t pH 6, in the absence of nitrite, gave no evidence of the formation of polymers; a t acid PH values (cn. PH 3 ) , coumaryl alcohol undergoes polymerization. so Reaction of Chalcones with Nitrous Acid.---In view of the structural similarity between derivatives of p-cournaric acid and those of benzalacetophenone (chalcone), it was of interest to examine the reaction of the latter compounds with H N 0 2 . Previous work had shown3that whereas p-coumaric acid is subjected to oxidative decarboxylation, the major product derived from the methyl ester of pcoumaric acid is the 3-nitro derivative. More recent work has demonstrated that this nitration depends on the presence of the phenolic hydroxyl group, since p-methoxycinnamic acid methyl ester does not undergo any observable change under comparable experimental conditions. p-Alethoxycinnamic acid appears to be coniwted by HXO. to products that exhibit maximum absorption a t longer wave lengths; however, 110 C 0 2 evolution was observed, and attempts to isolate a distinctive product were not successful.
I
I
1
I
I
Li 0
z a m
CT 0 v3
m
a
I
\-
I
I
, %
240 260 280 300 WAVELENGTH, m p
.4bsorption spectra of p-coumar>1 alcohol, 5 X 10-5 M (curve A ) , and of polymer (10 8 rng per liter) forineti b y t h e action of nitrite (curve E ) ; solvent, 95% ethanol, I -cni cells. Fig 2
~
As with the methyl ester of p-coumaric acid, the principal product of the reaction of 4,4'-dihydroxy(IO) K Freudenberg and G Gehrke, B e ? , 84, 443 (1961).
JOSEPH
S. FKUTON
\'d. 79
chalcone with nitrous acid was 3'-nitro-4,4'-dihydroxychalcoiie. The identity of this product was established by alkaline degradation t o p-hydroxyacetophenone arid 3-nitro-4-hydroxybenzoic acid. The possibility that the product was 4,4'-dihydroxy-3oxiininoflavanone l1 was excluded by comparison of the dimethoxy derivative of the product with an authentic sample of 4,4'-dimethoxy-3-oximinoflavonone. l 2 Similarly, with 2,4'-dihydroxychalcone, treatment with nitrous acid gave, a s the principal product, 3'-iiitro-~,4'-dihydrox).chnlcotlc. Experimental Reaction of Isoeugenol with Nitrite.---?'(, a solution of ?;ax02 (8.3 g., 0.13 mole) in one liter c i f 0.M Jf phosphate buffer (pH 6.0) was added, with stirring, a solutioii of isoeugenol (10 g., 0.06 niole) in 300 ml. of acetone. T h e rnixture became yellow and turbid after 5 inin., antl crystals separated from the solution after it had stood a t rooin temperature for 6 hours. After 30 hours, the precipitate (3.8 g.j was collected; after recrystallization from nicthaiiol it melted a t 132-133' (reported6 133-134'). Calcd. for C20H D O ~(326.4): C, 73.5; H, 6.7. Found: C, 73.2; €1, 6.8; mol. wt. (Kast method), 329. Treatment with p-nitrobenzoyl chloride gave the mono-p-iiitrobenzoyl ester, m .p. 154" (reported6 156-137O). Calcd. for CziH25SOi (475.5): X, 2.98. Found: K, 2.94. Treatment with dimethyl sulfate gave the monomethyl ether, m . p . 12&1263 (reportedc 126'). Upon treatment with concd. H2SOJ, the dimer gives a blood-red color, which is changed t o blue-grecri whcn mater is added. The compound gives L: light pink color with the phloroglucinol-HCI reagent. It is soluble in hot methanol, hot ethanol, chloroform, ethyl acetate a n d acetone. The absorption spectra of isoeugcriol and dchytlrodiisocueenol are shown in Fie. 1. The iiifrared sncctruin
The filtrate obtained by the removal of the er>-st:illiiie tic.liydrodiisoeugeitol was concentrated t o about 800 nil. antl chilled; :i yellow scilid (2 g.) separated. This product is extremely soluble in metlianol aiid is sparingly soluble in mater; it softeiis a t 90-110' dec. A determination of the apparent molecular weight by the IZast method gave a value of 985, suggesting t h a t it is composed, o n the average, of six G-units. The product \vas S-free (sodium fusioii, Kjeldahl analysis). On treatment n.ith pliloroglucinolHCl, the product gave a dark red color. The absorption spectrum of this material is given in Fig. 1. The filtrate obtained by the removal of the product tlcscribed in the preceding paragraph was concentrated t o dryness under reduced pressure, and extracted \vitli 30 ml. of methanol. From the niethanolic extract, a broivn p(iwder (0.5 g.1 was obtained, which gave a (lark-red color with plilorogluciiiol-HC1. n'hen a mixture of 100 1111.of 0.06 JI phosplicite lmffer (QIi 6.0) And a solutioii of 1 g. of isoeugenol in 30 nil. of acetone was kept a t rnom temperature for 2 d'iys, no crvstallization was noted. Reaction of b-Hvdroxvcinnamic Derivatives with H N 0 2 .- TO a solution b f ~ I m Oi . (0.57 miltiinole) of p-metIiosj-ciiiiiarnic acid methyl ester'3 (in.p. 88-89') in 50 ml. of tliowiiewater ( I : 1 by voluinci, 85 n g . [ I ,2 millitnoles) of Sah-02 w a s added, ;rntl the solution was ncidifictl t o p€I 2 with HC1. Spectroplitrtoinetric observation of the course of tlic r e x tiori showed no change in the ultraviolet absoriitioii spectruiii over a 2-lir. period, TYlien 0.34 g. (1 .:iniillimolrs) c d p iiietlioxyciiiiiairiic acidI4 in 100 nil. of dioxaue--watcr was treated with 0.18 g. of SaS02 ( 2 3 inilliinoles), :tiiii the solution was acidified t o pH 2, after n i i c hour thc ahsorl)tioti maximuin :it Xi0 nip shifted to :310 i:ip. witliiiut :i~i~)rccialilc (11) T%y analogy to t h c suggcstion th.rt a n oximino cc,niiic,tiiid i i :>I, intcrnietliate in t h e reaction of N-acetyldehyilr~,trrr,iiiiew i t h iiilroiis acid [G. Taborsky, P. S. C;iinm:rrata and J. S. I ; r u l o n , J . I$it,l. ( ' h c i i ~ . , 226, 103 (1957)l. (12) S. v . Kostanecki a n d hI. Widner, Hrv., 37, 4161 (190-I). (13) W. Will. ibid., 2 0 , 204 (1887). (14) T. Rotarski, ibid., 41, 1996 (1908).
Nov. 20, 1957
ETHYL-AND DIETHYLBENZENE FROM ALRYLRENZENE
change in absorbance. W o COZevolution was observed, and attempts to isolate a crystalline product were unsuccessful. Reaction of 4,4'-Dihydroxychalcone with HNOz.-To a solution of 4,4'-dihydroxychalcone15(2 g., 0.0083 mole) in dioxane (60 ml.) was added a solution of NaSOz (1.2 g., 0,0174 mole) in 60 ml. of water. The mixture was acidified with 5 N HC1 to p H 2 and shaken for 3 hours a t room temperature, and the crystalline precipitate that separated was filtered, washed with water and ethanol, and dried; m.p. 287-290'. Additional material (m.p. 28j-290') crystallized from the filtrate when it was allowed to stand a t room temperature for 8 hours. The orange-red product (total pkld 1.25 g.) was recrystallized twice from ethyl acetatebenzene; 1n.p. 290'. Calcd. for C I S H ~ I S O(285.3): S C, 63.2; H,3.9; N, 4.9. Found: C, 63.0; H , 4.1; S,4.7. On acetylation of 0.1 g. of the product with 4 ml. of acetic anhvdride in the Dresence of 0.25 e . of sodium acetate. a crystalline product (0.1 g., m.p. 160') was obtained. Calcd. for Cl9H1&07 (369.3): C, 61.7; H , 4.1; iY, 3.8. Found: C, 62.0; H , 4.1; X, 3.7. On methylation of 0.2 g. of the product with 0.4 ml. of dimethyl sulfate in the presence of methanolic KOH, the dirnethoxy derivative was obtained. After recrystallization from methaiiol, it melted a t 167' dec. Calcd. for C17HlsNOj (313.3): K , 4.5. Found: S , 4 . 5 . A mixed m.p. determination with an authentic sample of 4,4'-dimethoxy(m..p. 168-170" dec.) gave a melting 3-0ximinoflavanone~~ point of 140-143', showing t h a t the two compounds are not identical. Alkaline degradation of the product (1 9.) with 5070 K O H (15) T. A. Geissman and R. 0. Clinton, THISJ O U R N A L , 68, 697 (1946).
[COTTRIBUTION FROM THE
5953
(25 ml.) at 170-180" for 3 hours, followed by neutralization with COz, and extraction with ether, gave, upon evaporation of the ethereal solution, 9-hydroxyacetopheiione (m.p. 105', no depression of mixed m.p. with an authentic sample). The neutralized aqueous solution was acidified and extracted with ether; evaporation of the ethereal extract gave 3-nitro4-hydroxybenzoic acid (m.p. l a " , reportedlo 183'). Calculated for C7H5N06 (183.1): C, 45.9; H , 2 . 7 ; S , 7.6. Found: C, 46.1; H, 2.7; N, 7.4. The structure of the product obtained by treatment of 4,4'-dihydroxychalcone with HXOz is therefore 3'-nitro-4,4'-dihydroxychalcone. The dimethoxy derivative of this compound has been reported t o melt at 160" dec.lT Reaction of 2,4'-Dihydroxychalcone with HNOZ.-This chalcone14 was treated with HNOZin the same manner as the 4,4'-isomer to yield 1.8 g. of a product which, after recrystallization from ethanol, melted at 230". Calcd. for CIS&NO5 (285.3): C, 63.2; H, 3.9; N , 4.9. Found: C, 62.9; H, 4.1; N, 4.8. On acetylation, the diacetate (m.p. 9394') was obtained. Calcd. for CloHlsTO, (369.3): N, 3 . 7 . Found: N, 3.8. On degradation with alkali as above, followed by acidification and steain distillation, o-hydroxyacetophenone was identified by its ultraviolet absorption spectrum (as compared with that of a n authentic sample); after extraction of the residue with ether, 3-nitro-4hydroxybenzoic acid (m.p. 183') was isolated, indicating t h a t the product of the reaction with HNOs is 3'-nitro-2,4'-dihydroxychalcone. (16) P. Griess, B e y . , 20, 408 (1887). (17) P.Pfeiffer a n d B. Segall, A n n . Chem.. 460, 130 (1928). NEW
HAVEX. CONS.
RESEARCH DEPARTMENT, STANDARD
Disproportionation of Alkylbenzenes. IV. BY D. A. MCCAULAY
OIL
CO.
(INDIANA)]
Ethylbenzene and Diethylbenzene AND
A. P. LIEN
RECEIVED MAY27, 1957 In the presence of hydrogen fluoride plus excess boron trifluoride, ethylbenzene disproportionates rapidly and soon reaches a primary equilibrium having the composition: benzene, 45%; ethylbenzene, 10%; m-diethylbenzene, 45%. Little triethylbenzene is formed because the m-diethylbenzene takes on a proton and is tied up as a positively charged complex. However, a t higher temperatures or after longer times diethylbenzene gradually reacts and a new equilibrium is slowly approached containing four components: benzene, ethylbenzene, 1,3-diethylbenzene and 1,3,5-triethylbenzene. The equilibrium composition is found to be a function of the number of ethyl groups per benzene ring in the starting hydrocarbon mixture.
Ethylbenzene, in the presence of hydrogen fluoride plus excess boron trifluoride, disproportionates rapidly and almost completely a t room temperature into benzene and m-diethylbenzene. The completeness of reaction and the production of the meta isomer were attributed to the preferential formation of a complex of m-diethylbenzene with HF-BF3. Although diethylbenzene as well as ethylbenzene should accept alkyl groups, no triethylbenzene was formed. This result was surmised to be a rate rather than an equilibrium effect. As part of a continued study of the reaction, therefore, ethylbenzene and diethylbenzene were disproportionated with longer reaction times and a t higher temperatures. Under these more vigorous reaction conditions the product distribution was found to be different and to be a function of the ratio of ethyl groups to benzene rings present. Experimental Ethylbenzene, diethylbenzenes and triethylbenzenes from Eastman Kodak Co. were used without further purification. ( I ) D. A. McCaulay a n d A. P. Lien, THIS JOURNAL, 76, 2407 (19531; (111) 76, 2354 (10.54, ( V ) 79, 5808 (1957).
Commercial grades of hydrogen fluoride, 99.6% pure, and boron trifluoride, about 99% pure, were obtained from the Harshaw Chemical Co. T h e experiments were carried out in a 1000-ml. Hastelloy autoclave fitted with a 1725-r.p.m. stirrer. Hydrocarbon, hydrogen fluoride and boron trifluoride were charged t o the autoclave and the mixture was stirred at a controlled temperature. After reaction, the entire contents were withdrawn into crushed ice. T h e hydrocarbon product was separated into successive carbon-number fractions by distillation through a column of thirty theoretical plates. Individual fractions were identified by their physical properties and by spectrometric analysis.
Discussion The results obtained on treating ethylbenzene with hydrogen fluoride plus a large excess of BF3are given in Table I. At low temperatures and short reaction times the products are benzene and mdiethylbenzene. At higher temperatures and a t longer times, triethylbenzene appears and apof the mixture. The explanaproaches 25 mole tion for this behavior is t h a t the first step reaches equilibrium rapidly; because a large excess of BF3 is used, most of the primary product, m-diethylbenzene, is tied up as a positively charged aronium ion.
